Burger Quality Concern Greasiness

I have had a customer complaint for the Beef Burgers saying that they are quite greasy and are flaring up more than usual on the grill.

I confirmed the complaint by testing/cooking the samples from that exact lot and it was indeed a lot greasier than usual also smoke/flare was significantly high.

I checked fat levels - usual, raw materials - usual. The most astonishing part is that the shrink after cooking is also the same. So how come there is a lot more grease and flare ups than usual? Been manufacturing same burger with same formulation for over a decade now.

Any comments on it? Any one faced similar issue?

So, if the fat content and size of the patties are the same, my next question would be, has anything changed with the heat?

Quality of the gas used for cooking might be different, the amount of heat (is the temp the same?) and cleanliness of the grill or the deflector plate might be affecting the flare up of the meat.

How did you determine that it was greasier? 

No change with heat too. Complaint is from different locations and I confirmed with my grill at the facility.

Greasiness - We have been manufacturing these burgers for quite a long time and we do the cooking test for sensory evaluation very often on this product. This time, fat was dripping wet when usually it simply provides a mere appearance to look moist.

The balance of the kinds of fat present could result in a different rate of melting.  Low density and unsaturated fats could be exuded earlier in the cooking process instead of being trapped inside by the sear.  

Something as simple as what the cattle were fed could be the underlying difference.